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Avoid the Heat Pump Villain: Why Low-Loss Headers and Buffers Can Sabotage Your Heat Pump's Efficiency

Mars · 2024-01-23T06:00:00Z

Heat pumps are becoming increasingly popular as they provide an efficient and eco-friendly way to heat homes, helping us save money and protect the environment. However, to work best, they need the right setup. Sometimes, parts like low-loss headers and buffers, which are supposed to help, can actually reduce the heat pump's effectiveness. This can lead to less warmth and higher running costs. It's important to understand why these parts might not always be beneficial and what you can do to get the most out of your heat pump. The Two Pillars of Heat Pump Prowess Understanding how heat pumps operate holds the key to optimising their performance. Two fundamental principles guide their efficiency: 1. Low-Temperature Symphony: Think of heat pumps as musicians, capable of raising the temperature of heat, much like conductors orchestrate notes. But here's the twist: the lower the target temperature, the less energy they need to play their magic. So, aiming for a cosy 20C instead of a sweltering 25C translates to a lighter burden on the system and a lighter burden on your wallet. 2. Flowing River of Warmth: Heat pumps move heat through water flowing through your radiators and/or underfloor heating. Imagine this water as a river, where a smooth, steady current efficiently delivers the thermal energy. Now, picture what happens if you dam the river with restrictions like narrow pipes or sluggish pumps. The flow suffers, and the heat struggles to reach its destination, leaving you feeling chilly despite the pump working overtime.The Deceitful Decoys Low-loss headers and buffers are often recommended by many installers and manufacturers as beneficial additions to heat pump systems. They are touted to enhance efficiency and comfort. However, in practice, the benefits they promise may not always materialise as expected. Let's see why: Low-Loss Header Trap: These headers aim to minimise heat loss in the pipework, but they often achieve this by reducing the water flow. Remember our river analogy? A constricted header acts like a dam, hindering the smooth flow and consequently, the efficient transfer of heat. This leads to the dreaded high delta T situation – a large difference between the temperature of the water entering and leaving your radiators. It's like the conductor demanding the orchestra play at full volume while restricting the air to their instruments. The result? Strained performance and disappointing results. The Buffer's Misdirection: Buffers are essentially storage tanks for hot water, supposedly providing you with readily available warmth and reducing the heat pump's workload. But here's the catch: buffers add complexity and introduce additional heat loss points. They essentially become thermal cul-de-sacs, where some of the precious heat gets trapped and wasted. Additionally, buffers can encourage inefficient on-off cycling of the heat pump, further negating any potential gains.Beyond the Decoys: A Path to Optimal Performance So, how do you ensure your heat pump system lives up to its full potential? The key lies in simplicity and a focus on the two core principles we discussed earlier: 1. Embrace the Flow: Ditch the low-loss headers and any other flow-restricting components. Let the water flow freely, like a well-maintained river, ensuring efficient heat transfer throughout your home. 2. Befriend the Low-Temperature Symphony: Ensure your temperature control is managed directly by the heat pump's controller, as on-off thermostats can be less efficient than a buffer. It's crucial for the thermostat to be integrated with the system for optimal efficiency, rather than relying on standalone on-off mechanisms. 3. Weather Compensation – Your Wise Companion: Utilise weather compensation, a feature that automatically adjusts the heat pump's output based on the outdoor temperature. This ensures constant comfort while minimising energy consumption. Think of it as a dynamic conductor, adapting the orchestra's performance to the changing weather conditions. 4. Delta T – The Fine-Tuning Maestro: Implement delta T control, which fine-tunes the temperature difference between the flow and return water. This further optimises the heat pump's operation, squeezing out every drop of efficiency. Consider it the musical equivalent of perfect intonation, ensuring a harmonious performance from your heating system. 5. Radiator Harmony: Use thermostatic radiator valves (TRVs) only in bedrooms, allowing weather compensation and the heat pump itself to manage the temperature in common areas. This strikes the perfect balance between individual comfort and overall system efficiency. 6. Hot Water Wisdom: Optimise your hot water production too. Let the heat pump controller handle this task. Think of it as a bonus track in the symphony of energy savings. Avoiding the Heat Pump Villain Sometimes, navigating the world of heat pump installation can feel like a quest through a confusing landscape. If you're still daunted, consider buying my b...

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Air Source Heat Pumps (ASHPs)

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Mars

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Topic starter 02/05/2025 8:38 am

In light of the recent buffer tank/warranty comments in this topic, I’ve written this piece below. It’s a 10 minute read, but I think it warrants a dedicated video/podcast, because there’s a lot of ambiguity and grey areas here that need clarification.

https://renewableheatinghub.co.uk/fact-or-fiction-are-buffer-tanks-really-necessary-to-protect-your-heat-pump-warranty/

Pre-order: The Ultimate Guide to Heat Pumps

Subscribe and follow our Homeowners’ Q&A heat pump podcast

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Heatgeek

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02/05/2025 9:55 am

@potatoman As no one seems to be obliging, I attach a diagram. The idea is that only bypass flow goes through the tank when necessary so it is undisturbed by main flow. Connection to tank must be closely coupled.

Private individual. No affiliation with commercial "Heat Geeks" of same coincidental name.

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ASHP-BOBBA

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02/05/2025 10:02 am

@heatgeek is it that this design satisfies the manufacturers? its still (although balance by bypass) a double hydronic volumiser/buffer with 2 pumps

Professional installer. Book a one-to-one consultation for pre- and post-installation advice, troubleshooting and system optimisation.

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Heatgeek

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02/05/2025 10:14 am

@ashp-bobba I am afraid that you are talking to the wrong person about manufacturers preferences. However, as far as I can see, it functions the same as a 4 port buffer except that flow doesn't go through the top of the tank causing mixing, therefore I would have thought that it is a perfectly acceptable alternative to a 4-port.

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ASHP-BOBBA

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02/05/2025 10:57 am

@heatgeek Oh agreed, its a slightly better and slightly less resistive solution, perhaps even the middle ground of no buffer V buffer.

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Potatoman

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02/05/2025 12:53 pm

@heatgeek Thank-you for your reply, can you clarify the circulating pump situation, would you have to have 3 circulating pumps in operation, one in the heat pump and two in the design. Thanks

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ASHP-BOBBA

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02/05/2025 12:59 pm

@potatoman hi, the scheme detailed is 2 pumps, one for the ASHP (primary) and 1 for the secondary circuits.

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Heatgeek

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02/05/2025 1:04 pm

@potatoman No, the installation is exactly the same as a 4 port buffer with primary and secondary pumps except that the output flow bypasses the top of tank so as not to disturb the stratification of the tank. This removes some of the inefficiency problems associated with 4 port buffer tanks, like output temperature being reduced by mixing.

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Heatgeek

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02/05/2025 1:35 pm

Note a key point here though. The primary pump is connected in the return pipe while the secondary pump is connected in the flow pipe after the buffer tank to provide good hydronic separation between the primary and secondary pumps.

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Heatgeek

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02/05/2025 1:48 pm

Only the difference in flow between the heat pump and the emitters passes through the tank. This lower flow helps to preserve the stratification of the tank so that dilution of temperature to the emitters is minimised.

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Heatgeek

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02/05/2025 1:59 pm

Apologies. Poor choice of words. Delete "dilution of temperature to emitters is minimised".

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JamesPa

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02/05/2025 2:56 pm

Posted by: @heatgeek

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Note a key point here though. The primary pump is connected in the return pipe while the secondary pump is connected in the flow pipe after the buffer tank to provide good hydronic separation between the primary and secondary pumps.

That all sounds very believable. Presumably mixing of return water with flow water to the emitters (and thus a reduction of ft to emitters) will however still occur if the primary pump throughput is less than the secondary, so the requirement to set up properly remains albeit that it is less sensitive than a 4 port.

This post was modified 5 months ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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